1. Field of the Invention
The invention generally relates to electronics. In particular, the invention relates to wideband mixers.
2. Description of the Related Art
Ever since its inception in the early 1900s by Edwin Armstrong, RF mixer technology has been at the heart of radio technology. However the utility of mixers has typically been relatively narrowband in frequency range due to the usage of discrete components, such as inductors.
In the field of radio frequency integrated circuits (RFIC), a mixer circuit is usually implemented as a Gilbert cell type current commutating approach. See, for example, Gilbert, et al., Fundamentals of Active Mixer, Applied Microwave and Wireless, 1995, 10-27. However, other implementation methods are possible. In a conventional Gilbert cell type of mixer, the input devices are biased in the saturation region of operation. This is done to derive maximum V-I (Voltage-Current) efficiency at RF. The conventional approach is fraught with inefficiency, such as relatively poor-linearity and relatively high power dissipation. The conventional approach also uses on-chip inductors, which results in a narrowband design and a relatively large die footprint. In spite of these drawbacks, the conventional technique gained popularity due to first few generations of RFIC being captive to bipolar devices, which are very efficient V-I converters and excellent current commutators.
However, CMOS devices are typically not as efficient as bipolar devices as V-I converters. One approach is to use the CMOS devices to switch voltages instead of current. Such techniques have their share of drawbacks, such as relatively poor voltage gain, relatively high noise to folding of noise from high frequency into baseband or intermediate frequency (IF), and the like etc.
Apart from the technological limitations of CMOS devices, a modern receiver front end should have a relatively wide dynamic range to accommodate the near-far end problem (faint RF signal versus a large interfering signal). Also, battery-operated portable RF systems should be efficient at using power.